1. Field of the Invention
The invention relates to a method wherein the shape, form, position and configuration of a lesion or tumour, to be treated by a radiation therapy device, may be ascertained with greater definition, in order to better design a treatment plan for its eradication. In accordance with a further aspect, the invention also relates to method and apparatus for verification of the position of the lesion with respect to the radiation beam or beams prior to the execution of a radiation treatment. The invention relates to a method wherein the size, location and disposition of a tumour may be determined, updated and tracked prior to and during treatment therefor.
2. Description of Prior Art
The goal of modem day radiation therapy of cancerous tumours or lesions, is to eradicate the tumour while avoiding to the maximum extent possible damage to healthy tissue and organs in the vicinity of the tumour. Since the large majority of tumours are radioresponsive, they can be controlled or eradicated completely if a sufficient radiation dose is delivered to the tumour volume. However, the delivery of the necessary tumourcidal dose may result in certain complications due to damage of healthy tissue that surround the tumour, or due to damage to other healthy body organs located in the proximity of the tumour. Conformal therapy is a radiation treatment approach which attempts to combine accurate target localization with focused radiation delivery in order to conform the high dose region closely to the region defined by the outer surface of the tumour while minimizing the dose to surrounding healthy tissue or adjacent healthy organs. Various conformal therapy techniques are well known in the art.
Conformal radiation therapy employs dedicated radiation units capable of producing highly energetic radiation beams of photons, electrons or other charged particles. The radiation unit typically has a radiation source, which is typically mounted on a rotatable gantry of the radiation treatment unit. Through gantry rotation, the radiation source is rotated about the patient who is typically placed on a treatment table and the radiation beam is directed towards the tumour or lesion to be treated. Various types of devices are used to conform the shape of the radiation treatment beam to encompass tightly the outline of the tumour as seen by the radiation treatment beam as it traverses the patient's body into the tumour. An example of such a device is a multileaf collimator, which consists of a set of computer-controlled movable leaves or fingers, which can be positioned individually in and out of the radiation beam in order to shape it to the tumour outline. Various types of radiation treatment planning systems can create a radiation treatment plan which, once implemented will deliver a specified dose to the tumour while sparing the surrounding healthy tissue or adjacent healthy organs.
The basic problem in conformal radiation therapy is knowing the location of the target, or lesion or tumour, or alternatively of the healthy organs with respect to the intended placement of the radiation beam or field (I) prior to the design of a radiation treatment plan and (II) at the time of the radiation treatment. Localization of the target volume within the patient prior to the design of a radiation treatment plan is performed by acquiring a three-dimensional image of the patient with a conventional diagnostic imaging device such as computerized tomographic (“CT”) imaging device, a magnetic resonance imaging (“MRI”) device or a positron emission tomographic (“PET”) imaging device, as they are known in the art. These sophisticated devices may be available from a variety of manufacturers, such as GE Medical Systems, Marconi, Toshiba, Siemens, Phillips and others.
At the present time, when the treatment is initiated, both the patient's position and the position of the target within the patient at the time of the radiation treatment are assumed to be grossly the same at as they were at the time the treatment plan was created. However, if the position of the target volume is not correctly determined (I) prior to the treatment plan creation or (II) at the time of treatment, treatment failures can occur in a sense that the conformal dose of radiation may not be delivered to the correct location within the patient's body. Failures of type (I) can occur if the conventional imaging modality fails to reveal completely the shape, location and orientation of the tumour or lesion or organ of interest. This may occur since not all conventional diagnostic imaging devices adequately, completely or fully determine the exact shape, size and orientation of a tumour, resulting in that even with the use of the most up-to-date diagnostic imaging device, some tumours may not be fully diagnosed. Failures of type (II) can occur as a result of organ displacement (motion) from day to day, which may occur from a variety of factors, such as growth of the tumour, change in the patient physionomy due to weight loss, or even patient breathing. Failures of type (II) can also occur from incorrect positioning of the patient on the treatment table of the radiation treatment unit.
To avoid the above failures, present day radiation treatment plans typically regard the target of the radiation to occupy a space in the patient's body, which is larger than it really is, in order to ensure that the smaller tumour or lesion, will fall within the larger volume. As a result, some healthy tissue or healthy organs surrounding the tumour or lesion will be irradiated with the maximum radiation dose intended for the tumour or target. Delivering the maximum radiation dose to a larger volume of healthy tissue or healthy organs may increase the risk of damaging these, and may for example, promote future cancers in the healthy surrounding tissue. For this reason oncologists using present conformal radiation therapy may decide to deliver a lower radiation dose to the intended treatment volume in order to spare the non-target tissue with the potential disadvantage of compromising the success of the treatment by underdosing some portion of the target organ.
In an attempt to improve the localization of the lesion for the treatment of prostate cancer and therefore rectify failures of type I, a method was disclosed Holupka et al., U.S. Pat. No. 5,810,007 which utilizes a transrectal probe to generate a two-dimensional ultrasound image. This image is then superimposed on an image acquired with a conventional diagnostic imaging device, such as CT scan. The image registration in the above said method requires the identification of at least 2 fiducials visible in both the ultrasound image and the image acquired with the conventional diagnostic imaging device. However, the following shortcomings may limit the utility of the above said method:
1. The transrectal ultrasound probe may considerably displace the lesion or organ thus providing inaccurate information about the spatial location of the lesion at treatment time if at that time the transrectal probe is not re-inserted. In any event, the insertion and removal of the probe prior to initiating treatment may cause displacement of the lesion, adding further uncertainty to the localization of the tumour. Moreover, inserting the transrectal probe for each treatment session can cause significant patient discomfort, resulting in this method not gaining popularity with physicians.
2. Holupka provides only for two dimensional images, and assumes that the 2D ultrasound image and the image obtained with the conventional diagnostic imaging modality are acquired in the same plane. For this case two identifiable fiducials in both images would be sufficient to register and superimpose the images. However, there is no certainty that the ultrasound image and the image from the conventional diagnostic imaging device are providing images in the same imaging planes and therefore a deviation of one image from the plane of another may considerably compromise the accuracy of the method.
3. The above said method registers and superimposes a two-dimensional ultrasound image onto a 2-dimensional image acquired with a conventional diagnostic imaging modality. Thus the ultrasound definition of the lesion is performed only in a single plane. For the purposes of three-dimensional conformal therapy, a two-dimensional definition of the lesion is incomplete and therefore inadequate since in other imaging planes, the extent of the lesion volume may be larger or smaller.
4. Further, Holupka is of limited application since it may only be used with respect to a very limited number of tumours, such as of the rectum, lower large intestine, and of the prostate. It can not be used for other type of tumours.
In attempt to rectify failures of type II, another system was proposed to verify the target or lesion position prior to a radiation treatment session by Carol, U.S. Pat. No. 5,411,026. The system comprises an ultrasound imaging device to acquire at least one ultrasound image of the lesion in the patient's body and a device to indicate the position of the ultrasound image generating device or probe with respect to the radiation therapy device. The above said system verifies that the actual position of the lesion immediately before the treatment session conforms to the desired position of the lesion in the radiation treatment plan by comparing the outlines of the outer surface of the lesion as defined on the at least one ultrasound image to the outline of the outer surface of the lesion as defined on the at least one of the diagnostic images obtained by a computerized tomographic (“CT”) or alternatively by magnetic resonance imaging (“MRI”) device and used for the design of the radiation treatment plan. However, the following shortcomings may limit the utility of the above said system.
1. The appearance of the tumour or lesion or organ in the ultrasound image or images can have an appearance different from that of tumour or lesion or organ in the images obtained with conventional diagnostic devices. Thus the process of comparing outlines of the outer surfaces of the tumour or lesion or organ as they appear in images obtained with different imaging devices may be inaccurate since these surfaces can be different both in appearance and extent. In other words, Carol compares apples and oranges, which results in an incomplete assessment of the tumour. Since the trend in conformal treatment is towards more accurate spatial delivery of the exact dose of radiation, this shortcoming is quite significant.
2. Carol also does not address failures of type I whereby the diagnostic images obtained with computed tomography or magnetic resonance imaging devices do not reveal completely the location or the extent of the tumour or lesion or organ, due to the inherent limitation of said devices with respect to certain tumours in certain locations. Furthermore if the computed tomography or magnetic resonance diagnostic images do not reveal, or completely reveal, the tumour or organ or lesion, Carol will lack the means to outline an outer surface to serve as a reference for the comparison to the outer surface of the tumour or lesion or organ outlined on the one or more ultrasound images.
In view of the above description of the prior art it is therefore an object of the invention to provide an improved method and apparatus for radiation therapy treatments to decrease the rate of occurrence of the above defined failures of type I and type II.
It is another object of the invention to provide a novel method and apparatus for accurate localization, sizing and definition of tumour or lesion or other organ volume in preparation for radiation therapy.
It is an object of the present invention to provide for the use of ultrasound imaging at the planning stage of a treatment plan;
It is a further object of the invention to provide an improved method and apparatus for establishing an ultrasound image or plurality of ultrasound images for target definition and localization and correlating this image or plurality of ultrasound images to radiation therapy simulator images, obtained with conventional diagnostic imaging devices such as a computerized tomographic (“CT”) imaging device, a magnetic resonance imaging (“MRI”) device or a positron emission imaging device (“PET”), or any other type, such as for example future types of diagnostic devices.
It is also an object of the present invention to provide a novel method for three-dimensional superposition of a three-dimensional ultrasound image of a lesion onto another three-dimensional lesion image, such as CT or MRI or another ultrasound image.
It is yet another object of the invention to provide an improved method and apparatus for accurate positioning of the target relative to radiation therapy beams based on the registration of an ultrasound image or plurality of ultrasound images acquired immediately before or after the acquisition of conventional diagnostic images to an ultrasound image or plurality of images acquired immediately before a radiation treatment session.
The invention relates to a method and apparatus for (a) lesion localization and tumour or lesion or organ definition for radiotherapy treatment planning and (b) for verification and rectification of lesion position during radiotherapy treatment.